Unit dose detergent products are convenient for consumers, since there is no need for them to measure out the required volume of detergent each time. Various unit dose formats, including tablets, and containers made of water-soluble material, are already known. Water-soluble containers are attractive since they avoid direct consumer contact with the detergent contents which are potentially irritant, and can have a faster dissolution profile than tablets (because the detergent contents do not need to be compacted particles). Fast dissolution in the wash is often required to release active ingredients from dosage units to be consumed in a single dishwasher run, so that they can become effective as soon as possible, for instance before they are deactivated by the high temperatures of the wash. Containers are preferred for this reason, and also since they are capable of incorporating many more types of composition including liquid, gel and paste compositions, not just solid ones. With multi-compartment containers, more than one type of composition can be incorporated (e.g. one solid and one liquid composition), incompatible ingredients can be kept separate until use, compartments can be designed to release their respective contents at different times in the wash, and/or greater opportunities for improved aesthetics are provided.
In practice in the automatic dishwashing (“ADW”) field, the choice of available sizes and shapes of unit dose products is limited by the size and shape of machine dispensers into which they are to be placed. There is also a general demand in the art for more concentrated products which use less packaging and/or confer better performance by including higher amounts of active ingredients. It would therefore be useful to have a compact ADW unit dose detergent composition containing a high level of ingredients contributing to the performance.
When dealing with containers made from water-soluble material, it is also important to ensure this material does not dissolve or deteriorate prior to the intended usage point of the container. Adverse interactions between the container material and the container contents during storage can potentially lead to container deformation, loss of mechanical strength of the product and rendering it unattractive. For these reasons it is helpful for the detergent formulation inside the container to have a low water content. When space is an issue, it is also important to minimise the levels of carriers not contributing to performance in the wash, such as water. Nevertheless, whilst aqueous compositions are to be avoided, the composition must still be capable of dissolution in the wash, and ideally not leave residues on the dishware.
One particularly important type of ingredient in the context of detergent performance is a builder. Builders soften water by removing free cations from the water, thereby increasing the performance of other detergent ingredients which are adversely affected by those cations. Mostly, they react with calcium and/or magnesium ions to form complexes or precipitates. Historically, phosphates like STPP and KTPP have been the mainstay detergent builders, but there are increasing regulatory restrictions on the use of these ingredients worldwide.
Gel formats are visually very attractive to consumers, especially transparent gels. However, there is a conflict between the requirements for low water content, high builder content, and the gel not being opaque. Many available builders are solid at room temperature and do not dissolve in sufficient quantities in the non-water solvents typically used to produce anhydrous gels. For example, phosphates like STPP and KTPP and non-phosphate builders like MGDA and GLDA may be in dissolved form in an aqueous formulation, but may be in the form of dispersed particles in a non-aqueous formulation; dispersed particles can scatter light and render the formulation opaque.
Previously, if a unit dose detergent product was to contain a builder and a transparent fluid, this was usually achieved in the form of a multi-compartment container, carrying builder comprised in a solid composition and/or opaque fluid in one compartment, and a transparent fluid containing no builder in a separate compartment. However, the drive for higher performance and greater concentration of active ingredients has forced the present inventors to look for ways to incorporate builder in the transparent fluid too. In addition, liquids and low viscosity gels are liable to leak out of a container if the container material becomes damaged, so it would be desirable in this context for the transparent fluid to be a self-standing gel.
Certain types of polyacrylic acid (and salts thereof) can act as a builder (c.f. U.S. Pat. No. 3,904,685) and have been included as part of builder systems in commercial tablet and opaque gel ADW formulations. Their carboxylic acid/carboxylate groups allow them to chelate or form salts with the metal ions. As polyelectrolytes, they can also act as dispersants for soils, helping to prevent their redeposition on glass and dishware. For instance, compounds in the Sokalan™ PA range are advertised as dispersants. On the other hand, other types of polyacrylic acid may not have builder capacity, depending on the polymer structure. For example, cross-linked, high molecular weight polyacrylic acid (e.g. in the Carbopol™ range) has been used in low concentrations as a thickener for aqueous liquid ADW systems, together with a non-cross-linked, lower molecular weight polyacrylic acid salt as a builder (cf. U.S. Pat. No. 5,368,766).
Typically, a polyacrylic acid builder is synthesised in aqueous solution, and optionally then dried. Thus, the common forms that are commercially available to the detergent formulator are an aqueous liquid or a spray-dried powder. The formulator may use the powder directly in a tablet formulation, use the aqueous liquid directly in an aqueous liquid detergent formulation, or redissolve the powder in an aqueous liquid detergent formulation. However, there is great difficulty in dissolving high levels of polyacrylic acid builder in non-aqueous systems comprising high levels of non-ionic surfactants. Copolymers of acrylic acid and other monomers that have been tried may have a greater solubility in the surfactant composition, but show lower solubility in the wash liquor and lower performance as a builder.
WO 2004/099274 discloses the formation of a graft polymer in which a polyalkylene glycol forms the backbone, and poly(meth)acrylic acid is grafted as branches onto the backbone. Use of the graft polymer in automatic dishwashing is mentioned. The free radical polymerisation is carried out at 90° C. in the presence of the polyalkylene glycol and water which is charged into the system at a controlled time. The graft polymer is therefore formed in an aqueous system, which may optionally additionally contain an organic solvent. Accordingly, this could not be used directly to form a non-aqueous gel.
EP 0,639,592 discloses the formation of a builder which is a related graft polymer to the one of WO 2004/099274. The polymerisation reaction is carried out at 100° C. or higher in the presence of substantially no solvent of any type; the polyether is melted by heating, to allow the reaction to take place. The ratio of monomers to polyether is at least 0.25:1. Although the polymerisation reaction itself does not utilise a solvent, the polymer is subsequently neutralised using an aqueous base or dissolved in a water/alcohol mixture, such that the end result of the synthesis is an aqueous solution of the graft polymer. Accordingly, it could not be used directly in non-aqueous gels. Furthermore, the examples of detergents in this document are aqueous liquid detergents.
There is still a need in the art for a transparent/translucent, non-aqueous ADW gel containing significant quantities of a builder, preferably a self-standing gel of this type. Such a gel would be advantageous even when not incorporated in a water soluble container, for example if the gel is rigid and stable enough not to require encapsulation in a container.
The present inventors have discovered that polyacrylic acid and related acrylates can be synthesised directly in non-ionic surfactant, in the absence of water, to form an aesthetically appealing gel that is suitable for ADW use and affords good builder and surfactant performance.